Mechanical resonators can be used to measure the density or viscosity of fluids.
One possible application of such measurement systems is the monitoring of SF6 insulation gas in gas insulated electrical apparatuses such as medium or high voltage switchgear. However, because SF6 is a potent green house gas, governmental regulations are becoming stricter. This results in tighter licensing and operation requirements for plant owners. As a result, more precise monitoring technology is needed to be able to detect, e.g., SF6 gas leakage more precisely.
In other possible applications, the determination of concentrations of individual components in gas mixtures is the key goal. This problem can be addressed by measuring the total gas mixture pressure p, the total gas mixture temperature T, and the total gas mixture density ρ and deriving the component concentrations from these measurement parameters. If the concentration of one or more components in the gas mixture is low, however, or if a component's concentration has to be measured with higher precision, a more accurate density measurement system is required.
Other possible applications for density measurement systems are, e.g., the monitoring of chemical and pharmaceutical processes, energy content determination in gas metering, or higher precision altitude metering, e.g., for aeronautics.
EP 0 582 045 B1 and WO 2010043268 A1 describe methods and devices for measuring gas densities. These implementations are based on two resonantly vibrating quartz tuning forks which are low-cost parts in microelectronics. One of these quartz tuning forks is arranged in an evacuated reference chamber while the other one is in contact with the to-be-measured gas or gas mixture. Due to the interaction between the gas or gas mixture and the respective tuning fork, the resonance frequency of this tuning fork is shifted. The amount of this frequency shift is then used to derive a density readout value for the gas or gas mixture.
The disclosed methods and devices have the disadvantage, however, that gas density readings obtained from them are susceptible to frequently encountered fundamental errors. Thus, the density readout values are not as accurate as desired.